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TABLE XXXII. 



SrsTiMATic Survey oi the Chie? Stages in the Development 

 OP THE Human Eae. 



I. First Stage. 

 The auditory nerve is an ordinary sensitive skin-nerve, which, during the 

 differentiation of the horn-plate, appears at a certain point on the skin of 

 the head. 



II. Second Stage. 



The differentiated place of the horn.plate, at which the auditory nerve 

 appeared, forms a small special auditory groove in the skin, which has an 

 outer orifice in the appendage called the " labyrinth." 



III. Third Stage. 



The auditory groove has detached itself from the horn-lamina, and forms 

 a small closed auditory vesicle filled with fluid. The " labyrinth-appendage " 

 becomes rudimentary {Aquceductus vestibuli) . 

 IV. Fourth Stage. 

 The auditory vesicle differentiates into two connected parts, the ear- 

 pouch (utricuhts) and the ear-sac (^sacculus). Each of the two vesicles 

 receives a special main branch of the auditory nerve. 

 V. Fifth Stage. 

 Three semi-circular canals grow from the ear-pouch (as in all Amphi- 

 rhina). 



VI. Sixth Stage. 



The " snail " (^cochlea) grows from the ear-sac in Fishes and Amphibia ; 

 it is very insignificant, and is only developed as an independent part in the 



Amniota. 



VII. Seventh Stage. 



The first gill-opening (the blow-hole of Selachians) changes into the 

 tympanic cavity and the Eustachian tube ; the former is externally closed 

 by the tympanic membrane (Amphibia). 



VIII. Eighth Stage. 



The small bones of the ear (^ossicula auditus) (the hammer (malleus) and 

 anvil (incus) from the first gill-arch, the stirrup {stapes} from the second) 

 develop from parts of the first and second gill-arches. 

 IX. Ninth Stage. 



The external ear is developed, together with the bony ear-canal. The 

 shell of the ear is pointed and movable (as in most lower Mammals). 

 X. Tenth Stage. 



The ear-shell, with its muscles, becomes disused and a rudimentary 

 organ. It is no longer pointed, but, on the contrary, has a curved rim with 

 a small ear-flap (as in Anthropoid Apes and Men). 



